Stabilized lubricating compositions



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United States Patent STABILIZED LUBRICATIN G COMPQSITIONS James B. Peeso, Stamford, and -Edvvin:0..Hook, New Canaan, Conn.,.assignors to *American Cyanamid Com- 'pany, New York, N. Y.,,.-a-, corporation. of vMaine No Drawing. Application May31,'1952, I

=senarNo.-=291, s6

8 Claims. ,(Cl. 252-325) ,This invention relates to lubricating-oil:additives; to lubricating oil compositionsv containing the same; and particularly to those oils-of the type knownas crankcase oils. Although the improved lubricating oil compositions of the present invention are -highly desirable for use in the crankcases of passenger automobiles, ,theyiare also especially valuable for heavy duty-servicein truck, bus, aeroplane, marine-and dieseleengineswhich operate for long periods oftime at hightemperatures.

The principal objects of the invention are to provide an improved lubricating oil of the heavy duty type which is heat stable, which is particularly resistant to sludge formation and oxidation, which is-non-corrosive to alloy bearings and other metal parts under conditions of extreme service, and which is'free'from varnish formation and ring sticking tendencies.

When conventional lubricating oils are subjected to high operating temperatures for extended periods of time, as encountered in heavy duty service, they show a tendency to oxidize or decompose with the formation of complex and objectionable oxidation and decomposition "products. Under the high-temperature conditions obtaining in the engine, thesedecomposition products polymerize to form lacquer-like deposits on or between the moving parts oftheeng-ine causing them tostick or to wear rapidly. Even larger quantities ofpolymerization products remain dispersedinvthe partlywoxidized crankcase oil. and are-rapidly precipitated.=to'form a sludge when the engine. cools 1or. when'fresh .oil is added to the engine. These precipitated sludges become caked on the heated metal surfacesgand. cut 'down the effective life of the engine.

In United Statespatent applicationsSerial No. 1401; 960, filed July 11, 1941, and Serial:N0.-415,411, filed Octoberl7, 1941, now -abandoned,i-it isfdisclosedthat hydrocarbon lubricating oil compositions having ;greatly improved detergent, anti-corrosive and anti-sludge forming properties may be prepared -by ;the incorporation thereinof minor amounts of various organiosubstitute'd dithiophosphates. While the lubricating oils containing these organic substituted dithiophosphates are extremely resistant to .sludge formation underconditions of heavy duty service, we have foundthahwhen preparing these improved lubricating oil compositions from ordinary classes of lubricating, oils.which are not highly refined, a small amount of sludge Will form when the oil is-subjected to high temperatures in heavy duty service for long periods of time in the presence of air or oxygen. With the more highly ,refined oils, however, such as those treated by the solvent refining process, the amount of sludge formed undersuch conditions is small. Since it is desirable, however, to use a lower cost ,oilin trucks, buses, diesel engines, etc., which operate almost continuously at high temperatures, a further improvement in the heat stability of lubricating oils refinedby conventional methods is desirable.

We have found that these organic substituted dithiophosphates which are added to lubricating oilsrefined ice by ordinary methods mayibe rendered more heat stable and more resistant to oxidation and decomposition-and the lubricating oil compositions themselvesmade almost entirely resistantto sludge'formationin heavy duty-service for long periods of time atelevatedtemperaturesby the. incorporation therein of minor amounts of oil. soluble reaction products of phosphorus sulfides and wool grease, which reaction may be promoted by the-presence of a free oxygen-containing gas. -As used herein, these products will be. referred to as' oil soluble reaction products of phosphorussulfides or similar terms. i

The various dithiophosphates whichwerhavefound useful in improving: lubricating :oils andwhichmay be employed to advantage .with the oflesolub le reaction products of phosphorus sulfides-are thoseqhaving the general formula:

1 RO' s M a 1 R--O s n in which R is a member of the group consisting of:.aryl, alkyl, aralkyl, .cycloalkyl, aryloxyalkyl, :acylaryl and alkoxyaryl radicals; M is hydrogen sorha :salt-forming radical; and n is the valenceofsM. "More! specifically, compounds. of this class, include ,,the dialkyl dithiophosphosphates such as dibutyl,dithiophosphate,,dihexyl dithiophosphate, di n-octyl dithiophosphate, ,dicapryl di ztiophosphate, dilauryl dithiophosphate, dioc tadecy1 dithiophosphate, etc, We prefer to usehthose dialkyl dithiophosphates in which the alkyl group-:,-has from 5 to 30 -carbon atoms since the longer alkyl Chains-;-.tend to increase the solubility of the dithiophosphates in lubricating oils. The diaryl dithiophosphates and the diaryl dithiophosphates in which the aryl group bears an alkyl, .alkoxy or cycloaliphatic ;group are (13150 useful such as for example diphenyl .dithiophosphate, :di-(:2,4-'dia'myl phenyl) dithiophosphate, dikeryl zdiphenyl dithiophosphate (a product-obtained by treating:chlorinatedkerosene witha phenol in the presence of aluminum chloride and -then:reactin g.with P285) landsthe various-,di-(wax substituted diaryl) dithiophosphates as described inedetail, in application-Serial No. 415,411, filed October- 17, 1941, now, abandoned. We. also: prefer the alkyl group inlthe alkaryl radical to have 5 to 50 carbon atoms so that thecompounds are moreeasily. oil-soluble. We may also employ the dicycloaliphatic dithiophosphates-such as thosepreparedby reacting cyclopentanol, cyclohexanol, cy'cloheptanol, and methyl, ethyl, .propyl [and .am yl .substituted cyclopentanol, ,cyclohexanol and cycloheptanol, etc. with P285. Thediaryloxyalkyl .dithiophosphates such ,as di-(2,4-diamylphenoxyethyl) dithiophosphate, the diacylaryl dithiophosphates such as ,di-(lauroylphenyl);dithiophosphate and the dialkoxyaryl dithiophosphates may also be added to lubricating oils to improve the oxidation-stability of theoil.

We prefer to employ these various organic substituted dithiophosphates in the form of their metal saltsypref oi phosphorus sulfides should be employed. Theuamount ofboth of these substituents in the 'oil will also depend to some extent upon the purpose for which the oil is intended. For example an oil intended for extremely heavy duty service should contain more of both the dithiophosphate and the phosphorus sulfide reaction product as compared with the amounts required by an oil intended for ordinary usage.

The preparation and nature of the oil soluble reaction products of phosphorus sulfides such as of phosphorus sesquisulfide, phosphorus pentasulfide, etc., is set forth in United States Patents 2,483,571, issued October 4, 1949, and 2,375,060, issued May 1, 1945, and reference thereto is incorporated herein. The invention is particularly applicable to compositions comprising the organic substituted dithiophosphates, previously described, and to those reaction products of phosphorus sesquisulfide (P483) and wool grease.

The preparation of the oil soluble phosphorus sulfide reaction products will be further described in greater detail by the following specific example. It should be understood, however, that, although this example sets forth in particular detail some of the more specific features of such preparation, it is not to be construed as limitative thereof.

Material used:

Procedure The wool grease and butanol were charged to a 5 liter flask fitted with a stirrer, thermometer, and reflux condenser. The sodium hydroxide was dissolved in about its own weight of water and added. The reaction mixture was heated to 100 C. and held at that temperature for 70 minutes. The zinc chloride was dissolved in an equal weight of water and added to the reaction mixture which was then stirred for an additional /2 hour at 90-100" C. The reaction mixture was stripped to 120 C. under a water pump vacuum. The recovery of aqueous and non aqueous distillates was 58 g. and 158 g. respectively.

To the cooled stripped material 75.2 g. P483 was added and the temperature raised to 115 C. Air was blown through the Well-stirred reaction mixture at such a rate so as to maintain the exothermic reaction at 125-130 C. After one hour the exothermic reaction was over '(white fume evolution practically ceased) and air blowing was continued for V2 hour while maintaining the temperature at 125-130 C. by applying external heat. At this point 1000 g. S. A. E. oil, 150 g. barium oxide and 75 g. methanol were added. The reaction mixture was heated to methanol reflux and after -20 minutes became HzS-free. After heating an additional minutes the product was vacuum stripped to 120 C. After adding 60 g. Hyflo the material was poured while hot into a 1 gallon size precoated Sparkler Filter. The filtration required 65 minutes, using a final pressure of -35 lbs. and the cake was blown at 30 lbs. pressure for /6 hour. The yield of red-brown, haze-free product was 3059 g.

The excellent comparability and solubility of these oil soluble reaction products of phosphorus sulfides in hydrocarbon lubricating oil compositions containing the dithiophosphates leads to another important advantage, namely, the ease with which these compounds are blended with 4 the oil compositions. This step is further simplified by our practice of very. simply dissolving them in the lubricating oils up to the extent of 50% or higher concentrations for storage and shipping purposes. In this way the blender of the ultimate composition need only pour the additive composition into-the stock lubricating oil with suitable stirring in order to obtain the desired lubricant.

The invention will be further described in more specific detail by reference to and discussion of the following results obtained from heat stability tests which were run on various oil compositions selected to best illustrate the inventive concept.

These tests consisted of the following procedure: a 200 gram sample of the selected oil composition was placed in a 400 ml. short form, pyrex beaker and set in a partially ventilated oven which was maintained at 250 F. The test sample was observed at regular intervals during a hour period. 1 After 125 hours, the sample was removed from the oven and allowed to stand and cool for 24 hours. The sample was then observed for hazing, precipitation and/or gelling. Precipitating and/ or gelling were considered as failures; a small amount of precipitation, however, could be tolerated; hazing, although not a crucial factor, was an indication of heat instability.

The following results were noted on blends using a solvent refined Mid-Continent base oil, S. A. E. 10:

Zinc dihexyldi- Wool Greasethiophosphate, P483 Reaction Appearance of Oil Blend 7 percent product, percent 0. 0 (control) 0. 0 Clear, slight sediment. 0. 6 0.0 Black, opaque. 0. 6 0. 05 Clear, small crowfoot ppt. 0. 6 0.50 Do.

From the foregoing table, it will be realized that the addition of 0.6% zinc dihexyldithiophosphate alone rendered the oil blend unacceptable and a failure insofar as the heat stability thereof was concerned. The black, opaque appearance of the oil blend clearly indicated the lack of heat stability of the additive-containing oil. However, it is to vbe noted that the addition of as little as 0.05% of a wool greaseP4S3 reaction product immediately improved the heat stability of the additivecontaining oil so that the oil blend took on a clear aspect with merely a small crowfoot precipitate. A similar result was obtained when the concentration of the woolgrease-PrSs reaction product was increased tenfold from 0.05 to 0.50 percent.

From the foregoing, it will be seen that we have provided a lubricating oil composition comprising an organic substituted dithiophosphate and a heat stabilizer consisting of an oil soluble reaction product of phosphorus sulfide, which composition is heat stable, is particularly resistant to sludge formation and oxidation, is non-corrosive to alloy bearings and other metal parts under conditions of extreme service, and is free of varnish formation and ring sticking tendencies.

Although we have described but one specific preparation of the reaction products of phosphorus sulfides and have referred to, the results of specific tests of such a compound in lubricating oil compositions containing dithiophosphates, we consider the same not to be limited thereto. It is understood that suitable changes, variations and modifications may be made without departing from the spirit and scope of the invention.

We claim:

1. A hydrocarbon mineral lubricating oil composition comprising a hydrocarbon mineral lubricating oil and, as an antioxidant and anticorrosive agent having a tendency toward heat instability and the formation of sludge upon continued heating thereof at high temperatures,

5 0.1-3.0% by weight of a dialkyl dithiophosphate having the formula:

R-O s M R-O s n in which R is a member of the group consisting of alkyl radicals having from 5 to 30 carbon atoms; M is a polyvalent metal of the group consisting of calcium, strontium, barium, tin, zinc, magnesium, nickel, aluminum and cadmium; and n is the valence of M, said oil also containing, as a heat stabilizer for said dithiophosphate, 0.054% by weight of an oil soluble wool grease-phosphorus sulfide reaction product.

2. The invention as defined in claim 1, wherein the sulfide is phosphorus sesquisulfide.

3. The invention as defined in claim 1, wherein the dithiophosphate is a polyvalent metal salt of dihexyldithiophosphate.

4. The invention as defined in claim 1, wherein the dithiophosphate is a polyvalent metal salt of dilauryldithiophosphate.

5. The invention as defined in claim 1, wherein the 5 dithiophosphate is a polyvalent metal salt of dicapryldithiophosphate.

6. The invention as defined in claim 1, wherein the polyvalent metal is zinc.

7. The invention as defined in claim 1, wherein the 1 polyvalent metal is barium.

Cook et a1 Mar. 14, 1944 Williams et a1. May 1, 1945 

1. A HYDROCARBON MINERAL LUBRICATING OIL COMPOSITION COMPRISING A HYDROCARBON MINERAL LUBRICATING OIL AND, AS AN ANTIOXIDANT AND ANTICORROSIVE AGENT HAVING A TENDENCY TOWARD HEAT INSTABILITY AND THE FORMATION SLUDGE UPON CONTINUED HEATING THEREOF AT HIGH TEMPERATURES, 0.1-3.0% BY WEIGHT OF A DIALKYL DITHIOPHOSPHATE HAVING THE FORMULA: 